Polyhedral dice roller in Bash

roll.sh

#!/usr/bin/env bash
# Roll X dice with Y sides where $1 = "XdY" or "Y" and "X" is implied to be 1
# Inspired by Tippex x3
function roll() {
    local re="^([1-9][0-9]*)*([dD]{0,1}([1-9][0-9]*)){0,1}$"

    if [[ $1 =~ $re && ! $2 ]] ; then
        # Parse input
        local dice=1
        local sides=0

        if [[ ${BASH_REMATCH[1]} && ${BASH_REMATCH[3]} ]] ; then # E.g., "1d12"
            dice=${BASH_REMATCH[1]}
            sides=${BASH_REMATCH[3]}
        elif [[ ${BASH_REMATCH[2]} ]] ; then # E.g., "d12"
            sides=${BASH_REMATCH[3]}
        else # E.g., "12"
            sides=${BASH_REMATCH[1]}
        fi

        # Roll dice
        local total=0

        for i in $(seq 1 $dice) ; do
            local roll=$(shuf -i 1-$sides -n 1)
            total=$((total+roll))

            # Print each die if many dice
            if [[ $dice > 1 ]] ; then
                echo "Die $i: $roll"
            fi
        done
        echo $total
    else
        echo -n "ERROR! Usage: \"roll X dice with Y sides\" where \$1 = "
        echo "\"[Xd]Y\" and X and Y are both greater than zero."
        echo "E.g., \"1d12\", \"d12\", and \"12\" are all one 12-sided die."
    fi
}

roll $@